I have upgrade magento version after that i'm not able to save state (region), from both admin and frontend side into address edit section.
I have check customer's attributes and address attributes from admin and also try with apply reindex, deploy and other command.
I have also remove custom plugins, but still not able to save state (region).
When i select country like "Uganda" after that state dropdown replace with textbox and that textbox value can be saved but like "United states" country having dropdown so that dropdown value not able to save.
i have check state dropdown, there isn't any issue with state dropdown html code.